1. Field of the Invention
The present invention relates to automatic focusing methods used with photography and imaging equipment, and particularly to an automatic focusing method for a digital camera with high focusing accuracy.
2. Description of the Related Art
With the development of the technology of digital signal processing, digital cameras are now highly favored by consumers. Some digital cameras have focus adjusting mechanisms so that they can take high quality photos.
China Pat. No. 01202112 issued on Dec. 5, 2001 provides a camera module with a fixed focus. As represented in FIG. 4, the camera module 40 includes a substrate 41, an image sensor member 44, a tubular body 42, a lens member 43 and an elastic member 45. The lens member 43 and the image sensor member 44 are received in the tubular body 42 in that order from top to bottom, with the image sensor member 44 being held on the substrate 41. Aligned screw holes (not labeled) are defined in one end of the tubular body 42, the elastic member 45, and the substrate 41. Screws 46 are engaged in the screw holes, thereby attaching the tubular body 42, the elastic member 45 and the substrate 41 together.
To enable high quality photos to be taken, the image sensor member 44 should be positioned at the imaging plane of the lens member 43. The screws 46 are rotated inward or outward so that the elastic member 45 is compressed or decompressed, thereby adjusting the distance between the lens member 43 and the image sensor member 44. This is done until the picture captured by the camera module 40 is focused and clear to the human eye. However, the focusing procedure of the camera module 40 is rather laborious and time-consuming.
To solve the above-described shortcomings, many automatic focusing apparatuses and methods have been developed. However, typical automatic focusing apparatuses are assembled with a drive member having a predetermined accuracy of movement, which does not correspond to a depth of focus of a lens member of the automatic focusing apparatus. This may result in low quality photos. Therefore a new automatic focusing method is desired, which can conveniently and accurately adjust the image distance or the focal length of the digital camera.